1. Field of the Invention
The present invention relates to an optical sensing system, and more particularly, to an optical sensing system which uses a plurality of detectors installed at various positions next to an optical panel to generate a position signal for indicating the position of the optical panel.
2. Description of the Prior Art
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a perspective view of a prior art optical sensing system 10. FIG. 2 is a position signal table 22 of the optical sensing system 10.
The optical sensing system 10 comprises a rotatable circular panel 12, and a sensing device 14 for detecting rotations of the panel 12. The panel 12 comprises a plurality of encoding hole sets 11 discontinuously installed along various radial directions of the panel 12, and thus the sensing device 14 can generate a position signal 29 for each of the encoding hole sets 11 of the panel 12 in a discontinuous manner.
The sensing device 14 comprises three sensors 16, 18, 20 for detecting light passing through each encoding hole set 11 and generating correspondent sensing signals 24, 26 and 28. The three sensing signals 24, 26, 28 form a position signal 29 representing one position of the panel 12. Each encoding hole set 11 comprises one to three encoding holes arranged along one radial direction of the panel 12 and positioned along three circular tracks of the panel 12. The signal 24 generated by the sensor 16 at the outer track represents the least significant bit, and the signal 28 generated by the sensor 20 at the inner track represents the most significant bit.
If number of positions of the panel 12 is to be increased in order to increase the resolution of the optical sensing system 10, the maximum number of encoding holes within each encoding hole set 11 and also the number of sensors of the sensing device 14 have to be increased. Since the length of the inner track is much shorter than the outer track shown in FIG. 1, it is quite difficult to install more encoding holes along another track which is even shorter than inner track. Besides, when the number of sensors in the sensing device 14 is increased, its cost will be increased dramatically since the sensing device will have to be custom made.